Over 85% of Americans use caffeinated beverages daily, yet the reinforcing effects of caffeine have not been well-studied. In the first grant period, caffeine was shown to be a reliable reinforcer in a subset of coffee and soda users; i.e., some users consistently self-administered caffeinated beverages in preference to noncaffeinated beverages during repeated double-blind tests. Caffeine withdrawal also reliably occurred in several subjects. In the first three years of funding, we published 6 studies and 2 reviews, submitted 5 studies for review and have 4 manuscripts in preparation. We now propose to examine factors that might control the occurrence of caffeine reinforcement. The factors to be studied and the corresponding experimental questions are 1) Direct effects of caffeine: Will triazolam-induced fatigue and drowsiness increase the probability of caffeine reinforcement?, 2) Pharmacological specificity: Will theophylline and amphetamine substitute for caffeine reinforcement?, 3) Age: Is caffeine a reinforcer in children?, 4) Drug history: Is caffeine reinforcement especially common and robust in cocaine addicts?, and 5) Drug sensitivity: Will those who report adverse effects from caffeine reliably avoid rather than seek caffeinated beverages? In summary, this application will investigate several factors thought to control vulnerability to drug dependence (i.e., pharmacology, age of risk, dependence on other drugs and sensitivity to drug effects). One important mission of NIDA is to examine the dependence potential of licit drugs initially not thought to be dependence producing; e.g., nicotine and diazepam. We believe the study of caffeine falls within this mission of NIDA. Furthermore, since caffeinated beverages are so widely used and accepted, well-designed scientific studies about caffeine as a reinforcer are especially crucial to help make rational decisions about the dependence potential of caffeine.